“Catalyst‐on‐a‐Tape”—Teflon: A New Delivery and Recovery Method for Homogeneous Fluorous Catalysts

Abstract

There are intense efforts to develop new or improved strategies for recovering homogeneous molecular catalysts. [1] Many of these approaches are bi-or multiphasic in nature, and one particularly innovative method involves catalysts that are derivatized with (CH 2 ) m (CF 2 ) nÀ1 CF 3 ((CH 2 ) m R fn ) moieties or fluorous "ponytails". [2, 3] The initial applications of this now-familiar technique utilized perfluoroalkane solvents for recovery. However, the relatively high costs of such fluorous solvents, and other factors, pose limitations for industrial applications.Second-generation methods eliminated the fluorous solvent by exploiting the temperature-dependent solubilities of fluorous catalysts in common organic solvents. [4,5] Appropriately designed fluorous molecules are soluble only at elevated temperatures, and essentially insoluble at low temperatures. Such a thermomorphic character allows homogeneous catalysis at the high-temperature limit, and catalyst recovery by a simple liquid/solid-phase separation at the low-temperature limit. The presence of an insoluble fluorous support can be beneficial, for example, when small quantities are involved. Initial efforts have involved Teflon shavings [4] and fluorous silica gel. [6][7][8] We sought to expand the range of catalysts and fluorous supports that could be applied in such methods, and report herein a surprisingly effective procedure involving common commercial Teflon tape. This approach provides not only a convenient means of catalyst recovery, but also of catalyst delivery. From an engineering standpoint, tapes offer a variety of unique attributes, and it is reasonable to extrapolate that meshes and/or reactor parts, such as liners or stirring assemblies, could be fabricated with similar properties.As a test reaction, we selected the ketone hydrosilylation shown in Figure 1, which in earlier work was catalyzed by the fluorous rhodium complexes 1-R f6 and 1-R f8 in a liquid/liquid biphase system comprising an organic and a fluorous solvent.[9] The red-orange compounds 1-R f6 and 1-R f8 have very little or no solubility in organic solvents at room temperature.[10] However, their solubilities increase markedly with[*] Dr.

Insoluble Perfluoroalkylated Polymers: New Solid Supports for Supported Fluorous Phase Catalysis

“…Notably, Gladysz reported much higher rhodium leaching levels (run 1 -0.6%, run 2 -5%) when the more highly fluorophilic rhodium catalyst, [RhCl{P(CH 2 CH 2 C 6 F 13 ) 3 } 3 ], was supported on Teflon tape for ketone hydrosilylation. [12] …”

“…[7] Likewise, Biffis [8] and ourselves [9] reported signs of catalyst decomposition and the fluorous silica support changing colour in the solventless silylation of 1-octanol using dirhodium(II) perfluorocarboxylates and the hydrogenation of styrene with perfluoroalkylated analogues of Wilkinsons catalyst respectively, whilst Pozzis flu-orous chiral CoA C H T U N G T R E N N U N G (salen) catalyst was completely inactive for the hydrolytic kinetic resolution of terminal epoxides when it was supported on fluorous silica. [10] The problems described above have led us and others [11,12] to prepare new, non-silica based, well-defined, highly fluorinated solid supports for transition metal based fluorous catalysts. In this regard, Bannwarth reported high activities across two recycles for Suzuki coupling reactions using a perfluoroalkylated palladium(II) catalyst immobilised on perfluoroalkylated PEG dendrimers, but unfortunately without metal leaching data.…”

“…[11] In a parallel study, Gladysz described the use of commercial Teflon tape as an insoluble fluorinated support for facile separation of a thermomorphic rhodium hydrosilylation catalyst, in which catalytic activity was maintained over two recycles, but with some ligand (11%; cycle 1) and metal (5%; cycle 2) losses. [12] Here, we report the synthesis and applications of lightly cross-linked perfluoroalkylated polystyrene beads. Such systems are not only thermally robust and insoluble, but also chemically inert, something that will mitigate unwanted catalystsupport reactions.…”

Fluorous Chemistry

“…The most recent advance was the introduction of the fluorous release and catch concept [7]. A fluorous catalyst, which has limited or no solubility in the reaction mixture at room temperature and entrapped in a Teflon tape, is released to the reaction mixture at higher temperature, where it acts as a homogeneous catalyst.…”

Catalysis of Intramolecular Morita–Baylis–Hillman and Rauhut–Currier Reactions by Fluorous Phosphines; Facile Recovery by Liquid/Solid Organic/Fluorous Biphase Protocols Involving Precipitation, Teflon® Tape, and Gore‐Rastex® Fiber

“…[3,4] We then introduced the concurrent use of solid fluoropolymer supports, providing a locus for deposition. [3,5] In conceptually related recycling efforts, others have applied fluorous silica gel. [6][7][8][9][10] In two feasibility studies, we described (1) the use of Teflon shavings as a mechanical support for recycling the fluorous phosphine PA C H T U N G T R E N N U N G [(CH 2 ) 2 R f8 ] 3 , which is an effective Lewis base or nucleophilic catalyst for additions of alcohols to propiolate esters (n-octane, 65 8C), [3] and (2) the use of Teflon tape as an adsorbent for recycling a rhodium hydrosilylation catalyst derived from ClRh{PA C H T U N G T R E N N U N G [(CH 2 ) 2 R f6 ] 3 } 3 (dibutyl ether, 55 8C).…”